The present invention relates to test articles for use with digital signal magnetic recorders, particularly those of the helical scan type, and to methods employing the test sections on such test articles.
Diagnostic procedures and master test tapes have been used for years in diagnosing, testing, calibrating and adjusting digital signal magnetic recorders. Such digital signal magnetic recorders have usually been the so-called one-half inch tape drives, such as those tape drives sold by International Business Machines Corporation and identified by Model Nos. 2400, 2420 and 3420. Such magnetic tape drives or magnetic tape units employ vacuum columns for decoupling the reels of one-half inch magnetic tape from a tape driving capstan and recording-reproducing transducers. As such, the reel characteristics are isolated from tape driving performance with respect to the recording and reproducing transducers. Additionally, the vacuum columns of such tape units apply a positive pressure such that the one-half inch tape is usually held fairly close to the transducing gaps. Even with such favorable operations, difficulties arise in transducing operations because of debris on the magnetic tape, creases on the tape and variations of many parameters in such tape units. To that end, extensive diagnostic procedures have been employed in the maintenance programs as set forth in the above-referenced maintenance programs for the IBM 3803-3420 magnetic tape subsystem. These automatically employable test and diagnostic procedures usually require the recorder to be tested to record signals and then read such recorded signals back using particular procedures for analyzing tape unit performance, including readback and recording circuits. Also, a master tape was produced using stringent parameter control conditions for calibrating such tape units for facilitating recorded tape interchange between users of such tape units. That is, a tape may be recorded by one tape drive and the signals read from such tape by another tape drive. Tape drives may be manufactured by diverse manufacturers, hence, calibrating all of the tape drives by all manufacturers to a single master tape facilitates interchange of records between users having equipment made by such diverse manufacturers.
The so-called 1/2 inch tape has an aspect ratio of 2400 feet to 1/2 inch. Data processing requirements, with which such 1/2 inch tapes are widely used, have a high demand for rapid access to large amounts of data. Accordingly, it was desirable to change the aspect ratio by employing a shorter wider tape. Such tape has been incorporated into a tape-containing data cartridge as shown in commonly assigned U.S. Pat. No. 3,825,208, Ser. No. 318,954 filed Dec. 27, 1972, for reducing access time to a given set of signals recorded on a tape contained in the above-mentioned data cartridge. Automatic storage and retrieval techniques for such cartridges are employed. Such techniques are described in co-pending commonly assigned U.S. Patent application Beach et al, Ser. No. 198,877 filed Nov. 15, 1971. In such an apparatus, data cartridges are not only fetched from data cartridge storing storage cells but are also automatically loaded and threaded onto tape drives. Such automatic procedures indicate that some form of automatic diagnostics and parameter measurements are desirable for ensuring that the tape drives are properly functioning.
It also became apparent that the character of recording and reproducing had to change. While longitudinal tape transport, as used for 1/2 inch tapes, could be employed, cost and performance factors determined that a rotating head type of device, such as used on the well known video recorders and often termed helical scan recorders, were found to be more advantageous. Digital signal recording differs substantially from video recording in that an error condition cannot be tolerated in digital signal recording, as it is in video recording. Further, video recording uses frequency modulation techniques, while most digital signal recording uses so-called baseband recording. That is, the signals being recorded are not modulated onto a carrier before recording. Because of these substantial differences and the operational requirements for digital signals being substantially different from video recording, operation of digital signal helical scan recorders can be entirely different from the operation of video recorders. Accordingly, diagnostic procedures used for maintaining video recorders would not be necessarily applicable to digital signal recorders. Further, the error inducing or failure modes of such helical scan digital signal recorders appears to be substantially different from error modes of the longitudinally transported 1/2 inch tapes. Accordingly, new diagnostic procedures suitable for the new set of problems is required.
Some prior test techniques include logically arranging test procedures in an analytical array. For example, in 1/2 inch test tapes for 1/2 inch tape drives, one-hundred test records constituted a test file; several test files were serially recorded in one tape reel or volume. A set of signal perturbations of a first parameter were varied in a record-to-record manner within one test file. A second signal parameter was held constant in each such test file, but varied between successive files. In logically analyzing the test results, the test file varied parameter results were arranged along rows while the record to record changed parameters were arranged in columns. The records and files were read serially.
In unit record equipment, hole positions of test type unit record or tabulating (punched) cards were varied along orthogonal axes of the card. Only one parameter, hole position, was varied.